Humidity control of an electrical device

ABSTRACT

The invention relates to a device and a method for dehumidifying and control of humidity inside an enclosure comprising electrical equipment. The device comprises a heating element located to be in contact with the ambient air of the exterior of the enclosure and a cooling element located to be in contact with the ambient air of the interior of the enclosure. Dew condensed at the cooling element is guided to the heating element so that humidity from the air, condensed at the cooling element, may be transported to the heating element to be vaporised wherein the water guiding means comprises a capillary structure. In still another aspect of the invention, the functionality of the heating and cooling elements may be switched so as to reverse the flow of water and provide a humidity control arrangement.

TECHNICAL FIELD

The invention relates to a device and a method for dehumidifying andcontrol of humidity inside an enclosure comprising electrical equipment.

BACKGROUND

Electric equipment which is intended to be located where it might beexposed to humid environment or water is often protected by a waterproofenclosure. However, there might be small entrances, e.g. gaps, smallholes or diffusive leakages, through which water might enter into theenclosure. To make these cabinets completely waterproof is often acostly procedure and in many cases water, e.g. mist or humid air, mayenter into the cabinet already when the product is brand new. Even ifthe products are made completely waterproof they may be defect due todegradation at normal use, unexpected impacts or violence on the productor exposure to the environment, e.g. sun, wind and rain, which may leadto a degradation of the water proof protecting system so that water orhumid air may enter into the cabinet. There is also a risk that moistureor water will come into the cabinet when it is opened for maintenancework. For whatever reason moisture is trapped inside the cabinet, themoisture will cause corrosion problems inside the cabinet if thehumidity not is controlled.

The size of the cabinet intended to be dehumidified by the presentinvention may be in a wide range of varying sizes, e.g. from 2 to 500litres (0.002 to 0.500 cubic metres). These sizes represent a largenumber of different low power dissipating equipment for which a longterm corrosion protection is desired. For dehumidification of equipmentof such sizes as discussed above, it is usually difficult to installdehumidification or ventilation devices generally used in the field ofdehumidification. These devices usually comprise some kind of activedehumidification unit, e.g. heating elements, fans and venting conduits,and are in general rather bulky and hard to fit into small spaces. Therather complex construction of such a system also makes them expensiveand an advanced construction further contributes to a risk thatsomething in the construction may malfunction and need to be serviced atirregular times in order to work. In many cases, the cabinets for whichthe dehumidification device is intended to be used are located atinconvenient places or distant from the maintenance personal which makessuch maintenance work costly and time consuming.

As of today, one commonly used type of protection for the inside of anenclosure, comprising electric equipment, is to use watertight seals andattach a drying capsule with an absorbent which absorbs the moistureinside the enclosure. This way of making the equipment make the freedomin designing the enclosures of the equipment rather limited since it isimportant that the sealings are diffusion tight in order to have a lowmaintenance cost. In such a system, it is often hard to know how todimension the dehumidification device in order to not become unnecessaryspace requiring while still having a sufficient load capacity in orderto not need to be changed to often. In order to function in a desiredmanner there is either a need for some kind of indicating system whichindicates when the absorbent is full or some kind of regular servicewhen the absorbent shall be checked and may be switched if desired. Ineither case there is a need to physically open the enclosure and replacethe dehumidification capsule. Regardless of how such a dehumidificationdevice is dimensioned there will always be a maintenance need toregularly exchange the drying capsule in order to keep the moisturelevel in the enclosure below acceptable levels. The long-term cost willtherefore be high due to the need of maintenance personnel to check thecapsule on site and perform a change when necessary.

There have been suggested some other solutions to the problem withmoisture associated with electric equipment which do not involve adrying capsule. One solution is described in U.S. Pat. No. 6,196,003 inwhich a heating element is used for dehumidifying oil filled electricalapparatuses in order to protect the oil from water. In DE 25 349 09 adehumidification system for a substation for a mobile network connectionis described. According to the idea disclosed therein, a sensor is usedas dew point detector which switches on a heater in the substation whendew is detected. However, it is not disclosed how the moisture isremoved in these systems but merely how they prevent the moisture fromcondensing and thus not provides a dehumidified environment for theelectrical equipment.

Also EP 368 382 describes a device for dehumidification of an enclosurecomprising electrical equipment in which the moisture is removed fromthe inside of the enclosure. In this device, a cooling element islocated to be in contact with the air inside and condense dew from theinside air to be collected in a receptacle wherefrom it is allowed to beguided through a conduit out of the enclosure. However, this device willprobably not work very efficient unless there are quite large amounts ofwater to be condensed. In case there are small amounts of water to becondensed, there will most probably be a problem of transporting thecondensed water to the outside. First, in order to make the droplets tofall down into the receptacle, they need to be of a certain size beforethey will start to travel down by gravity for example. Furthermore, ifthe outlet conduit is too small, the water may adhere to the inside ofthe conduit due to capillary forces. On the contrary, if the conduit istoo big, moisture in the form of humid air may enter into the enclosurefrom the outside.

Hence, there is a need for a better dehumidification unit which is stillrather small to be fitted into the enclosure without any majormodifications. Preferably, the dehumidification shall be able to workcontinuously without any necessary periodical maintenance work. Evenmore preferably, the dehumidification unit will allow the enclosure tonot necessarily be completely water tight in all sealing so as to allowa greater freedom of design and avoiding a need of over duly precisionin the manufacture of the enclosure and its connecting edges.Furthermore, there is a need for an improved dehumidification systemwhich will work satisfactorily in transporting the condensed water fromthe inside to the outside of the enclosure.

SUMMARY

The present invention provides an improved device and method in order toachieve a satisfactory dehumidification of the inside of an enclosurecomprising electrical equipment so as to prevent corrosion due to wateror mist present in the enclosure. According to the invention, adehumidifier comprising a heating element and a cooling element ismounted in connection with the enclosure in such a way that the coolingelement is located to be in contact with the ambient air of the interiorof the enclosure and the heating element is located to be in contactwith the ambient air of the exterior of the enclosure. The dehumidifieris further provided with water guiding means which guides dew condensedat the cooling element to the heating element so that humidity from theair, condensed at the cooling element, may be transported to the heatingelement to be vaporised there. In order to provide an improved watertransport, the water guiding means comprises a capillary structure.

This solution provides a simple arrangement for dehumidifying the airwithin a cabinet. The invention may be used for all kind of electricalequipment contained in a box or the like. One field of use may forexample be base stations in a telecommunicating network.

According to an embodiment of the invention, the capillary structure isin contact with the heating element and adapted to guide water condensedat the cooling element to the heating element. The capillary structuremay for example be a mat.

By using a capillary mat which is in contact with the heating element itwill be possible to use the suction forces of the capillary mat to suckwater to the heating element as water is vaporised at the same. Anadvantage by using capillary forces for the transport of water is thatsuch a distributing system can work without being obliged to transportwater by the use of gravity or any kind of pumping equipment. In thiscase, the water transport will mainly depend on the vaporisation ratewhich will free the capillaries at the heating element from water andthereby sucking new, condensed water to the heated capillaries. In thiscontext, it is meant by “capillary mat” any kind of capillary structurewhich is able to suck a liquid by capillary forces.

In addition to have a first part of a capillary mat which covers atleast a part of the surface of the heating element so as to vaporisecondensed dew at the hot side, the dehumidifier may be provided with asecond part of the capillary mat which covers at least a part of thesurface of the cooling element so as to absorb dew condensed at the coldside. The first and second parts of the mat are connected to each otherby water guiding means. In a certain embodiment, the water guiding meanswhich connects the first part and the second part of the capillary matmay comprise a third part of the mat.

It shall be noted that the three parts of the mat may be either separatepieces or one entity comprising different regions. Furthermore, it mightbe advantageous to not provide the whole surface of the cooling elementand/or the heating element with the mat. For example, allowing a part ofthe cooling surface not to be covered with the capillary structure willallow the condensing efficiency to increase since the cooling elementwill be in direct contact with the ambient air and not being insulatedby the mat.

However, it is not necessary that the dehumidifier comprises the secondand third capillary mat. In an alternative embodiment it may be possibleto collect dew condensed at the cold side in a receptacle to which apart of the first capillary mat is in contact with. Preferably thisreceptacle is located below the cooling element so that the water willdrop into the receptacle by means of gravity. The first capillary matwill then by capillary forces transport the collected water to theheating element whereby the dew is vaporised to the exterior of theenclosure.

In an embodiment of the invention, the heating element and the coolingelement are formed as one entity having a first surface and a secondsurface wherein the heating element is located at the first surface andthe cooling element is located at the second surface.

In a certain design, the surfaces are made as ordinary, flat surfaces.In this case, the element is preferably made as a relatively flat platehaving the heating element and the cooling element located at oppositesides. In order to prevent heat transfer between the two sides, theplate may be provided with an insulation layer between the two sides.

To be noted, by surface is not necessary meant a flat, continuousstructure but may for example on the micro structure scale comprise aporous structure, microfibers or fibers, wave shaped elements or of anydesired shape having micro-structural irregularities. Furthermore, onthe macro structural scale the elements may be spherical, cylindrical,concave or convex, flat with holes in it or of other geometrical shapes.

When the heating and cooling elements are constructed as one entity, theentity may comprise a peltier element which induces a heating element atone side and a cooling element at the other side. This embodimentprovides the advantage of having one element which naturally creates aheating element and a cooling element when it is powered by DC.

In case the heating and cooling elements are constructed as one entity,e.g. a flat peltier element, wherein the first surface and the secondsurface are located opposite to each other, the third part of thecapillary mat may be located at the outer side of the entity so as toguide water between the first part and the second part of the mat. Thismay be achieved by wrapping a capillary mat or structure around theentity (peltier element) so that the heating element, the coolingelement and at least one edge part of the entity is covered by the mat.This provides an easy structure to produce and a relatively smallelement to be mounted to the enclosure.

In another embodiment, the cooling and heating entity is provided withone or several holes connecting said first, heating surface and saidsecond, cooling surface. In this way, water may be guided from a firstpart of the mat located at one side through the holes to a second partof the mat located at the second side of the mat. A desired number ofholes are preferably provided with a third part of the capillary mat inorder to facilitate the transport of water from the cold side to the hotside.

In a similar embodiment as the one described above, i.e. an elementcomprising one or several holes connecting the first surface and thesecond surface of the cooling and heating entity, it is not necessary toprovide the heating and cooling surfaces with a capillary mat but onlythe holes are provided with a capillary mat. However, the capillary matin the holes are located in such a way that the capillary mat is incontact with the heating element and the cooling element within theholes so as to form one or several capillary columns for wicking ofcondensed water from the cold side to the warm side to be vaporised. Itis of course also possible to make an embodiment which is a mixture ofthis embodiment and the foregoing one, i.e. to provide either the sidecomprising the heating element or the cooling element with a part of acapillary mat. For example, it might be favourable to provide the coldside with a capillary mat so as to absorb the condensed water in orderto avoid water to drip from the cooling element and thus remain in theenclosure.

In the foregoing embodiments, the invention has been described ascomprising a single element comprising both the heating element and thecooling element. It shall be noted that the principle of the inventionwill also work if the heating and cooling elements are separate unitswhich are located at different locations. This might be favourable inview of constructional aspects in certain applications and also have thebenefit of better isolating the heat and cold sources. However, in mostapplications, the combination of the heating and cooling elements as oneentity will have the benefit of a compact and simple design with a shortdistance for transport of water between the elements.

The dehumidifier may be located at different locations in or inconnection to the enclosure. In one embodiment the heating element andthe cooling element are mounted in or adjacent to an outer wall of theenclosure. In case the heating and cooling elements are constructed asone entity, having its cooling side on the opposite side of the heatingside, the element is preferably incorporated as a part of an outer wallof the enclosure, having its cooling element on the inside and itsheating side on the outside.

As an alternative, the heating element and the cooling element may bemounted inside the enclosure whereby said heating element is connectedto the outside of the enclosure via an air vent duct. In order toprevent re-vaporised water from re-entering the air inside theenclosure, the air vent duct should be tight to not allow the airleaving the enclosure to be in contact with the inside air of theenclosure.

In case the heating element and the cooling element are provided asdifferent entities, it is of course possible to locate them at differentlocations, e.g. to locate the condensing element in the interior of theenclosure and the heating element adjacent to the wall in such a waythat moisture will vaporise directly in the air exterior to theenclosure.

Hence, the present invention provides a dehumidification arrangementwhich is essentially maintenance free and can be fully automated inrespect of humidity control and power consumption. Furthermore, theinventive arrangement will work without any moving parts and will besilent which makes it particularly suitable for all kind of domesticappliances or any kind of devices where a low level of noise is desired.Due to its simplicity, the arrangement will provide a reliablearrangement with little risk of failure or break down. The arrangementcan also easily be scaled with respect to the size of to the enclosureand the drying capacity needed. Due to its relatively small size, thearrangement can easily be mounted on and integrated in existingenclosures with no or less efficient dehumidification devices. In thecase of a compact, plate shaped heat and cooling device, e.g. a peltierelement, it may be mounted in an outer wall or a lid for the enclosureand can easily be fitted to the enclosure by replacing the original wallor lid.

In addition, the dehumidification unit may be provided, if desired, withadditional features such as a hygrostat in order to only be active whenthe humidity is above a certain level.

In order to achieve a more efficient dehumidification, the device mayalso be provided with a fan. However, such equipment will make thedehumidifier more complex and space requiring and is not required formost applications. If applied, the fan should usually not provide astrong flow of the air but rather a gentle mixing or stirring of the airinside so as to provide transport of humid air to the vicinity of thecooling element.

It shall also be noted that the invention could be useful for thereverse function, i.e. if the heating and cooling elements are switched.In the case of using a peltier element the cooling side and the heatingside can easily be switched by changing the poles of the electricity.Hence, for example, a peltier element which is located in or near thewall could condense water from the outside and vaporise it on the insidein order to humidify the air inside the enclosure. By controlling thepoles, for example in response to a hygrostat, the invention may be usedto control the humidity of the interior air of the enclosure to bewithin a desired interval.

The invention further relates to a humidity control process for anenclosure comprising electrical equipment, said humidity control processcomprising the steps of:

-   -   providing a cooling element located to be in contact with the        ambient air of the interior of the enclosure so as to condense        moisture from the ambient air    -   providing a heating element located to be in contact with the        ambient air of the exterior of the enclosure    -   providing water guiding means which guides dew condensed at the        cooling element to the heating element        whereby moisture condensed at the cooling element will be guided        to the heating element to be vaporised at the heating element so        as to dehumidify the air of the interior of the enclosure.

In a specific embodiment of the humidity control process is thecondensed water transported for at least a part of its way from thecooling element to the heating element by means of capillary forces.

The humidity control process, which is mainly intended to be operated inorder to dehumidify the air inside an enclosure, may also be used forthe reversed function, i.e. to humidify the air inside the enclosure.This may be achieved in an easy way by switching the functionality ofthe heating element and the cooling element so that the flow of watermay be reversed so as to humidify the air of the interior of theenclosure. In this case, the humidity control process preferablycomprises a hygrometer which measures the humidity in the air andcontrol the system to dehumidify the air when the moisture content ofthe air is above a certain level and reverse the function to humidifythe air when the moisture content is below a certain value. An easy wayof changing the functionality of the heating and cooling element is touse a peltier element, which comprises both elements, and change thepoles of the current.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention will be described with reference to thefollowing figures which disclose:

FIG. 1 An enclosure for electric equipment comprising a dehumidifier

FIG. 2 a A schematic view of the positioning of a heating and coolingelement according to a first embodiment of the invention

FIG. 2 b A schematic view of the positioning of a heating and coolingelement according to a second embodiment of the invention

FIG. 2 c A schematic view of the positioning of a heating and coolingelement according to a third embodiment of the invention

FIG. 2 d A schematic view of the positioning of a heating and coolingelement according to a fourth embodiment of the invention

FIG. 3 A schematic view of a dehumidifying element

FIG. 4 A schematic view of the water transport in the element in FIG. 3when in use

FIG. 5 A schematic view of a variant of the embodiment of thedehumidifying element in FIG. 3

FIG. 6 a A second embodiment of a dehumidifying element

FIG. 6 b A first version of the embodiment of the dehumidifying elementshown in FIG. 6 a

FIG. 6 c A second version of the embodiment of the dehumidifying elementshown in FIG. 6 a

FIG. 7 A dehumidifying element comprising a peltier element

DETAILED DESCRIPTION

In the following, different embodiments of the invention, i.e. a devicefor dehumidification of the inside of an enclosure comprising electricalequipment, will be described with reference to the figures. Theembodiments (figures) aim to clarify how the different parts of theelements of the dehumidifier, e.g a heating element and a coolingelement, may be mounted in connection with the enclosure and how thedifferent constructive details of the dehumidifier.

As a general rule in these figures, solid arrows (when not associatedwith a number) indicate the flow of water or condensed humidity, i.e.water in liquid state. Dashed arrows indicate the flow of humid air ormist, i.e. the flow of water in a gaseous state.

FIG. 1 is a simple schematic overview of the intended use of adehumidifier 2 and shows an enclosure 1 for an electric equipment (notshown) comprising a dehumidifier 2 which is located in an outer wall 13of the enclosure.

In FIG. 2, as FIG. 1 only shows a very brief general overview, a moredetailed description of the dehumidifying arrangement is shown,exemplifying different ways of locating the different parts of thedehumidifier in the casing and how they are connected. FIGS. 2 a-ddiscloses four different ways of placing the heating element 3 and thecooling element 4 in an enclosure 1 is shown schematically. In FIG. 2 a,it is shown that the heating element 3 and cooling element 4 areconstructed as one entity and located in the outer wall 2 of anenclosure. The cooling element 4 is located on the outside, or formingthe outside, of the outer wall. The heating element 3 is located on theinside, or forming the inside, of the outer wall 2. The moisture in theair inside the enclosure 1 will condense at the cooling element 4 and betransported to the heating element on the outside of the outer wall 2and thereby be vaporised. The mechanism of transporting the condensedwater from the cooling element to the heating element in this case willmake use of a capillary structure which will be shown and explained inassociation with other figures.

In FIG. 2 b, another design of the dehumidifier is shown. The heatingelement 3 and the cooling element 4 are still constructed as one singleentity but is located inside the enclosure 1. The heating element 3 isprotected from the air inside the enclosure 1 by a casing 14 which isconnected to an air ventilation duct 13. The casing 14 of course alsoprotects the interior air of the casing 1 to come in contact with airexterior to the casing so as to prevent humidity in fresh air to enterinto the enclosure 1. Except for guiding the air through the airventilation duct 13 instead of releasing it directly to the fresh air asdescribed in FIG. 2 a, this configuration works according to the sameprinciple as described therein.

In FIG. 2 c, the heating element 3 and the cooling element 4 areseparate units. It is therefore necessary to include some kind of waterconduit 5 for transporting the condensed water from the cooling element4 to the heating element 3. As can be seen in the figure, the heatingelement 3 is located inside the enclosure 1 and is protected from theair inside by a casing 14. When the condensed water reaches the heatingelement 3, the water will be vaporised and released into the exterior ofthe enclosure through ventilation holes in the outer wall 12 at the partof the wall where the casing 14 function as a protective shield for thesurrounding air to enter into the enclosure 1. As an alternative, theheating element could also be located at the outside of the outer wall12 and thereby eliminate the need of having a casing 14 which shieldsthe heating element 3 from the air inside the enclosure 1. If desired,the elements could be located the reverse way also.

In FIG. 2 d, the heating element 3 and the cooling element 4 areseparate units as described in FIG. 2 c and a water conduit 5 transportswater between the elements. This configuration differs from the onedescribed in FIG. 2 c in that the cooling element is located inside theenclosure 1 (not adjacent to the outer wall 12). It is thereforeincluded an air ventilation duct 13, connected to a casing 14 enclosingthe heating element 3, which guides the vaporised water in to the openair.

In the schematic FIGS. 2 a-2 d, it is not in detail described how thewater is transported between the cooling and heating element. In thecases the elements are located at a distance from each other theconnecting may be an ordinary water conduit or a capillary column forexample. Examples of how the transportation of water can be arrangedwhen the elements are constructed as one entity will be described below.

FIGS. 3-7 shows more in detail different embodiments of how the heatingand cooling elements forming part of the dehumidifier may be designed asone entity.

In FIGS. 3 and 4 a first embodiment of such an element is shown wherethis entity is formed by a compact heating-cooling core surrounded by awater guiding material. The element shown in FIG. 3 comprises a heatingelement 3, a cooling element 4 and water guiding means in the form of acapillary mat 6 a-6 c so as to form one heating and cooling entity 7comprising all elements needed for condensing, transporting andvaporising water. As can be seen, the capillary mat 6 is divided into 3parts whereof the first part 6 a is in contact with the surface 8 of theheating element 3, the second part of the capillary mat 6 b is incontact with the surface 9 of the cooling element 4 and the third partof the mat 6 c is connecting the first part 6 a and second part 6 b ofthe mat. As shown in this figure, the third part of the mat 6 c is onlyconnecting the other parts of the mat 6 a, 6 b at one edge part of theheating and cooling entity 7. The capillary mat 6 could of course coverone or several more of the edges so as to increase the connectionbetween the first and second parts 6 a, 6 b. Furthermore, the mat mustnot cover the complete surface but may also cover a part, being providedwith holes or forming strips so as to reveal a part of the heating orcooling surfaces. In particular it might be advantageous to omitcovering the complete cooling surface 9 in order to expose the coldsurface 9 to the ambient air so as to improve the condensing effect.

In FIG. 4, it is shown how the cooling and heating entity 7 will workduring use. Moisture from the air within the enclosure will condense onthe capillary mat 6 at the part of the mat 6 b which is located at thecold surface 9 of the cooling element 4. The mat 6 will absorb themoisture which will be spread in the mat 6 due to capillary forces whichstrive to reach equilibrium of humidity in the mat 6 and moisture willstart to travel towards the dry parts of the mat. Hence, the liquid willstart to move from the part of the mat located at the cold side 6 btowards the part of the mat located at the hot side 6 a via theconnecting part 6 c. Due to the heating element 3, moisture which hasreached the part of the mat 6 a located at the hot surface 8 of theheating element 3 will start to vaporise. The vaporisation will makethis part of the mat 6 a dryer than the other parts of the mat 6 a, 6 bso that there will be a continuous stream of water or moisture towardsthe hot side of the element 7. To be accurate, the stream of water willcontinue as long as the relative humidity is lower at the hot side thanon the cold side. Due to the temperature difference between the hot andcold side of the element, the absolute humidity in the air on the hotside may be larger than on the cold side while the relative humidity onthe cold side will be higher due to the fact that hot air may be morehumid before condensing. Hence, there will be a flow of water from thecold side to the hot side until there is equilibrium of the relativehumidity on the outer and inner side near the respective surfaces.However, since the heating and cooling of the elements need to besupplied with some kind of energy in order to function, there is a wishto control the element to switch off when there is no need to dehumidifythe air inside the enclosure. The dehumidifying system may be providedwith an arrangement which measures the humidity in the enclosure, e.g. ahygrometer, which is connected to a switch which turns on and off thedehumidifier depending on the humidity, i.e. a hygrostat. The switch mayalso measure the humidity inside and outside the device since there is arisk that humidity may enter into the enclosure through this arrangementwhen there is a higher relative humidity outside than inside. In orderto prevent humidity from entering the enclosure, the device mayautomatically switch on when the relative humidity is higher outsidethan inside. This problem could also be adjusted by some otherpreventive mechanism, e.g. some kind of mechanical arrangement whichcloses the possibility of water to enter into the enclosure. It isfurther obvious that the heating and/or cooling elements not must becompletely switched on or off but may have a variable effect eitherchanged step less or by predefined steps to achieve a desired effect andthereby a controlled humidity in the enclosure.

As can be relatively easy understood, this arrangement provides an easyway for changing the flow of moisture to work in the opposite direction.The only thing which is needed to be done is to switch the heatingelement and the cooling element. An easy way of doing such a switch willbe discussed more in detail in association with FIG. 7.

As already mentioned in the general description part, it is notnecessary that both the hot side and the cold side are provided with amat. In FIG. 5 an alternative embodiment is shown. In this embodiment,humidity in the air condenses at the cold surface 9 of the coolingelement 4 in such a way that droplets 16 will merge on the cold surface.Due to gravity, the droplets 16 will travel downwards to be collected ina receptacle 15. At the other end of the receptacle, it is in contactwith a capillary mat 6. This capillary mat consists of a major part 6 awhich is in contact with the surface 8 of a heating element 3. Hence,the condensed water will travel through the capillary mat 6 to theheating element where it is vaporised and released into the open air.

However, this embodiment will probably work better when there is arelatively large amount of moisture from the air to be condensed. Smalldroplets tend to stick to the cold wall and will not start to fall downuntil they have reached a certain size.

As shown in this embodiment, the capillary mat only covers the surfaceof the heating element and having a part of it reaching into thereceptacle so as to be able to suck water from the receptacle to theheating element by capillary forces. By this construction there is noneed to cover both sides of the heating and cooling entity 7 with acapillary mat. In addition, the condensing efficiency will be very goodsince the cooling element will be in direct contact with the air.Another advantage of this construction is that it may work as a moisturetrap. If the hygroscopic pressure is larger outside than inside, waterwill start to travel from the outside to the inside, however, watercoming to the inside will accumulate in the receptacle 15 and thuscreate a high hygroscopic pressure relatively quick resulting in theundesired flow of water from the outside to the inside will stop.

In an alternative of this embodiment the capillary mat could of coursecontinue all the way and cover the lower edge part of the heating andcooling entity 7.

Still another embodiment of the heating and cooling elements of adehumidifier is shown in FIG. 6. FIG. 6 a shows a perspective view of aheating and cooling entity 7 which is shaped as an essentially flatplate having a heating element 3 located at one side and a coolingelement 4 located at the opposite side is provided with holes 10.

In FIG. 6 b, which is an intersectional view of the heating and coolingentity 7 in FIG. 6 a, the holes 10 are provided with a capillary mat 6which forms capillary columns 11 so as to connect the hot side 3 withthe cold side in order to transport water condensed at the cold side 4to be vaporised at the hot side 3.

FIG. 6 c shows an intersectional view of the element described in FIG. 6a in which the element 7 has been provided with a capillary mat 6 on thehot side 3 and the cold side 4 as well as in the holes 10. As describedearlier, condensed water at the cold side 4 will absorb into the mat 6 bat the cold side, be transported by capillary forces through the part ofthe mat 6 c located in the holes so as to form a capillary column 11.The water will be vaporised from the part of the capillary mat 6 alocated at the hot side 3 of the cooling and heating entity so thatwater will be dragged from the cold side 4 to the hot side 3.

A combination of the embodiments shown in FIGS. 6 b and 6 c is alsopossible, i.e. only one of the sides is fully or partly covered by acapillary mat.

In FIG. 7 is described how the heating and cooling elements of a compactdesigned entity as described in FIGS. 3-6 may be made and the heatingand cooling entity 7 comprising a heating side 3 and a cooling side 4 isexemplified as a peltier element 17. The element 17 comprises an anodeconnection 18 and a cathode connection 19. When there is a DC currentapplied to the connections 18, 19, the element will start to work andthe sides 3, 4 of the element 17 will start to get hot respectivelycold.

If there is a desire to reverse the process, the poles may be changed.By doing this, the cold side and hot side will switch. This means thatthe inventive concept of the idea does not only provide an efficientdehumidification device but also an efficient humidity controller. Ifthere is a desire to keep the humidity within a desired range in theenclosure, the system may be provided with a hygrostat and means foralternating the current depending on the value of the hygrostat. Whenthere is a desire to dehumidify, the element in contact with theinterior of the enclosure will be the cold side and thereby condensingwater which will be guided to the outside. On the other hand, if thereis a need to humidify the air inside, the poles may be changed and theelement will condense water on the outside and transport it to theinside where it is vaporised. Such an arrangement is in particularsuitable for the embodiments where both sides are equally designed, e.g.the embodiments shown in FIGS. 3, 4 and 6. The embodiment shown in FIG.5 will not work equally efficient in both directions and is moresuitable to be used only as a dehumidification device.

1. A dehumidifier for an enclosure comprising electrical equipment, saiddehumidifier comprising a heating element and a cooling element, saidcooling element located to be in contact with the ambient air of theinterior of the enclosure and said heating element located to be incontact with the ambient air of the exterior of the enclosure, saiddehumidifier further provided with water guiding means which guides dewcondensed at the cooling element to the heating element so that humidityfrom the air, condensed at the cooling element, may be transported tothe heating element to be vaporised wherein the water guiding meanscomprises a capillary structure.
 2. A dehumidifier according to claim 1wherein the capillary structure is in contact with the heating elementand adapted to guide water condensed at the cooling element to theheating element.
 3. A dehumidifier according to claim 2 wherein a firstpart of said capillary structure covers at least a part of the surfaceof said heating element so as to vaporise condensed dew at the hot sideand a second part of said capillary structure covers at least a part ofthe surface of the cooling element so as to absorb dew condensed at thecold side, said first and second parts of the capillary structure areconnected to each other by water guiding means.
 4. A dehumidifieraccording to claim 3 wherein the water guiding means connecting thefirst part and the second part of the capillary structure comprises athird part of the capillary structure.
 5. A dehumidifier according toclaim 2 wherein said heating element and said cooling element is formedas one entity having a first surface and a second surface, said heatingelement located at the first surface and said cooling element located atthe second surface.
 6. A dehumidifier according to claim 5 wherein saidentity comprises a peltier element.
 7. A dehumidifier according to claim4 wherein said first surface and said second surface of said heating andcooling entity are located opposite to each other and said third part ofthe capillary structure is located at the outer side of the entity so asto guide water between the first part and the second part of thecapillary structure.
 8. A dehumidifier according to claim 4 wherein oneor several holes are provided in said cooling and heating entityconnecting said first surface and said second surface of said coolingand heating entity and said third part of the capillary structure islocated in said at least one hole so as to guide water between the firstpart and the second part of the capillary structure.
 9. A dehumidifieraccording to claim 5 wherein one or several holes are provided in saidcooling and heating entity connecting said first surface and said secondsurface of said cooling and heating entity, said holes being providedwith a capillary structure in such a way the capillary structure is incontact with the heating element and the cooling element so as to formone or several capillary columns for wicking of condensed water from thecold side to the warm side to be vaporised
 10. A dehumidifier accordingto claim 2 wherein said heating element and said cooling element aremounted in or adjacent to an outer wall of the enclosure.
 11. Adehumidifier according to claim 1 wherein said heating element and saidcooling element are mounted inside the enclosure whereby said heatingelement is connected to the outside of the enclosure via an air ventduct.
 12. A dehumidifier according to claim 2 wherein the functionalityof the heating element and the cooling element are switched so that thedehumidification process is altered to provide a humidification process.13. A humidity control process for an enclosure comprising electricalequipment, said humidity control process comprising the steps of:providing a cooling element located to be in contact with the ambientair of the interior of the enclosure so as to condense moisture from theambient air providing a heating element located to be in contact withthe ambient air of the exterior of the enclosure providing water guidingmeans which guides dew condensed at the cooling element to the heatingelement whereby moisture condensed at the cooling element will be guidedto the heating element to be vaporised at the heating element so as todehumidify the air of the interior of the enclosure wherein thecondensed water during at least a part of its transport from the coolingelement to the heating element is transported by means of capillaryforces.
 14. A humidity control process according to claim 13 wherein thefunctionality of the heating element and the cooling element may beswitched so that the flow of water may be reversed so as to humidify theair of the interior of the enclosure.